Why does plaster of Paris harden when water is added?
Answer and explanation
Correct answer: It changes into gypsum
The hardening of plaster of Paris is a hydration reaction. Calcium sulphate hemihydrate, CaSO₄·½H₂O, combines with water and changes back into gypsum, CaSO₄·2H₂O. Gypsum forms an interlocking solid mass, making the paste hard. No sodium chloride, gas, or sugar is produced, so option A is correct.
Frequently asked questions
What is the correct answer to this question?
It changes into gypsum
Why is this the correct answer?
The hardening of plaster of Paris is a hydration reaction. Calcium sulphate hemihydrate, CaSO₄·½H₂O, combines with water and changes back into gypsum, CaSO₄·2H₂O. Gypsum forms an interlocking solid mass, making the paste hard. No sodium chloride, gas, or sugar is produced, so option A is correct.
Which subject and chapter does this question cover?
This is a Class 10 Science question. Chapter: Chemical Substances – Nature and Behaviour. Topic: Acids, Bases, and Salts.
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